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Swollen, knob-like structure
- The stigma is a swollen, knob-like structure. It can be either hairy or sticky, or sometimes both to trap pollen grains. In wind-pollinated flowers, like grasses, it may be feathery and branched or elongated. However, for some other flowers, it may be compact and has a sticky surface.
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Pollination is the act of transferring pollen grains from the male anther of a flower to the female stigma.
The characteristics of stigmas are vital for plant reproduction as they directly influence pollination success and genetic diversity. By having varied stigma shapes, sizes, and textures, plants can attract specific pollinators or increase compatibility with particular pollen types.
- Introduction
- Pollen and Stigma Cellular Functions
- Pollen and Stigma Structural Diversity
- Conclusions
- Acknowledgments
Angiosperm reproduction is highly selective. Female tissues are able to discriminate between pollen grains, recognizing pollen from the appropriate species while rejecting pollen from unrelated species (or from the same plant in self-incompatible species). This selectivity is accompanied by tremendous diversity in the cell surfaces of male and fema...
Overview of Structures
Mature angiosperm pollen grains are unusual vegetative cells that contain within themselves sperm cells, complete with cell walls and plasma membranes. This arrangement is accomplished soon after meiosis, when an asymmetric mitotic division produces a large cell that engulfs its diminutive sister, the generative cell (Twell et al., 1998; Yang and Sundaresan, 2000). Subsequently, the generative cell undergoes a second mitosis to form the second sperm cell required for double fertilization; “tr...
Pollen Adhesion to the Stigma: First Contact
To capture pollen grains, stigmas engage biotic and abiotic pollinators (such as insects and wind) and use rapid and strong adhesive interactions to retain pollen grains. The pollen–stigma interface can differ from species to species as a result of the wide variability in the morphology and content of stigma exudates, exine layers, and pollen coats. Several different methods have been devised to investigate and measure pollen–stigma adhesion (Stead et al., 1979; Luu et al., 1997a, 1997b; Zink...
Pollen Hydration: Activating Metabolism
Most pollen grains are metabolically quiescent and highly desiccated, ranging from 15 to 35% water content, when released from the anthers (Heslop-Harrison, 1979a; Buitink et al., 2000). Water immediately surrounds grains that land on a wet stigma, but those that land on dry stigmas mobilize their lipid-rich pollen coat to form an interface between the two cell surfaces. This interface converts to a histochemically distinguishable form thought to promote water flow (Elleman and Dickinson, 198...
Pollen Walls: Generating Structural Diversity
Patterning events that affect exine sculpting and aperture position also occur during or soon after meiosis. Haploid pollen typically produces a primexine, establishing an early pattern. After callose wall degradation, diploid tapetal cells elaborate this pattern with their deposition of sporopollenin material (Paxson-Sowders et al., 1997). Temporally regulated construction and degradation of the callose wall that surrounds pollen occurs in angiosperms (Heslop-Harrison, 1971; Munoz et al., 19...
Pollen Structure and Delivery
Pollen grains are transported to the stigma by a variety of biotic and abiotic mechanisms, for which their structures are believed to be uniquely adapted (Ackerman, 2000; Dobson and Bergstrom, 2000; Lunau, 2000). In some flowers, the selection for attracting animal pollinators is so strong that pollen grains are produced that are infertile and that function only for pollinator attraction and reward. Such grains are seen in Lagerstroemia, whose dimorphic anthers produce blue fertile pollen and...
Diversity in Pollen Coat Composition
The structure of the pollen coat also is adapted to different delivery mechanisms. Insect pollination is correlated with an abundant pollen coat (Pacini and Franchi, 1996). For example, the Brassica pollen coat can constitute 10 to 15% of the mass of the pollen grain (Dickinson et al., 2000). By contrast, grains carried by the wind often have a more limited coating, such as that seen among the grasses (Heslop-Harrison, 1979b). Because lipids appear to be necessary at the interface between pol...
Here, we surveyed recent discoveries of pollen and stigma functions, including (1) pollen adhesion, a multiphase process that is initially independent of protein–protein interactions but later involves pollen coat proteins; (2) pollen hydration, a step for which the presence of lipids, whether provided by the male or the female surface, likely modu...
We are grateful to members of the Preuss laboratory, especially Kiera Von Besser, Mark Johnson, and Ravishankar Palanivelu, for their helpful discussion and review of this article. We also thank horticulturalist Steven Meyer at the Lincoln Park Conservatory, Chicago Park District, for flowers with tetrad and polyad pollens. This work was supported ...
- Anna F. Edlund, Robert Swanson, Daphne Preuss
- 2004
The stigma is fixed to the apex of the style, a narrow upward extension of the ovary. The stigma (pl.: stigmas or stigmata) [1] is the receptive tip of a carpel, or of several fused carpels, in the gynoecium of a flower.
Nov 21, 2023 · The stigma consists of the sticky surface at the top of a flower's pistil. Stigmas come in a variety of shapes and sizes. They can be long and slender or more rounded with...
Sep 21, 2017 · On top of the style is the stigma, which is sticky and has the shape of a bulb. The size of the stigma varies from plant to plant and some are easier to see than others. In some flowers, the stigma is hard to see, whereas in flowers like tulips, the stigma is easily seen.
